A “dirty bomb” is a conventional explosive such as dynamite packaged with radioactive material that scatters when the bomb goes off. A dirty bomb kills or injures through the initial blast of the conventional explosive and by airborne radiation and contamination. At present there are no non-destructive methods of cleaning porous surfaces, for example concrete, of the radioactive contamination. Present decontamination methods would mechanically remove or ablate the top several mm of a porous contaminated surface. Under the current threat of a dirty bomb attack, it becomes important to develop a method for the decontamination of large surface areas without resorting to mechanically altering the surface.
Cesium-137 is a radioactive material which might likely be one of the radioactive materials of choice for utilization in a dirty bomb because of its generally wide availability due to its use in industrial instrumentation. Cesium is very soluble and is often found in chloride powder form that is highly dispersible. Once in contact with a porous surface, the cesium is expected to be both attached as particulate to the surface and also dissolved into the pore structure or bound to ion exchange sites within the surface. Surface decontamination, other than mechanical removal, might consist of washing the surface with copious amounts of water, but this would require that the contaminated water be recovered to prevent further environmental contamination. A chelating agent might be added to the wash water to remove some of the contamination from the surface, but it might also promote ingress of the contamination deeper into the pore structure. Other radioactive elements include the actinides, more particularly, the transuranics, although not as readily available as Cs-137. Both Sr-90 and Co-60 are other radionuclides that are available for dirty bombs.